Method and apparatus for transmitting broadband amplitude modulated radio frequency signals over optical links

Abstract

An optical communications system including a plurality of modulated radio frequency carriers which span more than an octave in bandwidth. In one implementation, the carriers are grouped into ranges which span less than octave in bandwidth and separately transmitted over uique optical links. In another implementation, the groups are multiplexed on one optical link by using different wavelengths. In still another implementation, several of the bands are up-converted to the highest band of interest and then transmitted, either over single or multiple links. The resulting signals are demodulated and then down-converted before they are recombined into the broadband signal in excess of an octave in bandwidth.

We claim: 
     
       1. A method for transmitting a plurality of radio frequency channels covering more than one octave of bandwidth from a first location to a second location, said method comprising the steps of: selecting two or more groups of contiguous radio frequency channels, each of said groups covering a bandwidth of less than one octave;   generating a plurality of optical signals at said first location, each optical signal corresponding to one of said groups;   modulating the intensity of each optical signal with the radio frequency channels of its respective group;   transmitting each resulting modulated optical signal to the second location via a separate optical link; and   demodulating each transmitted optical signal at the second location into its respective group of radio frequency channels.   
     
     
       2. The method of claim 1 wherein said optical signals generating step comprises: generating a plurality of optical signals of different wavelengths at said first location wherein each of said optical signals corresponds to one group of radio frequency channels.   
     
     
       3. A method of transmitting a plurality of channels of information from a first location to a second location said method comprising the steps of: defining two or more groups of channels wherein each channel is assigned to at least one of said groups;   modulating a radio frequency carrier signal with each channel in each group, wherein each radio frequency carrier signal uniquely identifies one channel in a group;   generating a plurality of optical signals, each corresponding to one of said groups of channels;   amplitude modulating each of said optical signals with the modulated radio frequency carriers corresponding to its respective group of channels;   transmitting each of said optical signals to the second location via an optical link unique to that optical signal;   demodulating each of said optical signals at the second location into its respective modulated radio frequency carrier signals;   converting at least one of said modulated radio frequency carrier signals to a different frequency band of carrier signals which does not overlap with any other transmitted radio frequency carrier signals; and   combining the resulting modulated radio frequency carrier signals in a single signal.   
     
     
       4. The method of claim 3 wherein said optical signals generated step comprises: generating a plurality of optical signals of different wavelengths.   
     
     
       5. A system for transmitting a plurality of channels of information from a first location to a second location, said system comprising: an optical transmitter including means for receiving signals corresponding to each channel of information, means for generating a plurality of radio frequency carrier signals, means for generating a plurality of optical signals, means for modulating each of said information signals onto at least one of said radio carrier frequencies to produce respective modulated radio frequency carrier signals, means for selecting a first group of said modulated radio frequency carrier signals, none of which have the same radio carrier frequency, means for selecting a second group of said modulated radio frequency carrier signals, none of which have the same radio frequency carrier, means for modulating a first optical signal with said first group of modulated radio frequency carrier signals, and means for modulating a second optical signal with said second group of modulated radio frequency carrier signals;   an optical receiver including means for demodulating each said optical signal into its respective modulated radio frequency carrier signals, and means for combining said modulated radio frequency carrier signals into a single signal; and   a plurality of optical links connecting each of said optical signal modulating means with a respective one of said optical signal demodulating means.   
     
     
       6. The system of claim 5 wherein said optical signal modulating means comprises: means for generating a plurality of optical signals of different wavelengths.   
     
     
       7. The system of claim 5 wherein said optical link comprises: a unique strand of optical fiber connecting each optical signal modulator to its corresponding optical signal demodulator.   
     
     
       8. The system of claim 5 wherein said receiver further comprises: means for converting at least one of said modulated radio frequency carrier signals to a frequency which is different from the frequencies of any other of said radio frequency carrier signals.   
     
     
       9. A transmitter for transmitting a plurality of channels of information comprising: means for receiving signals corresponding to each channel of information;   means for generating a plurality of radio frequency carrier signals;   means for generating a plurality of optical signals;   means for modulating each of said information signals onto at least one of said radio frequency carrier signals to produce a respective modulated radio frequency carrier signal;   means for selecting a first group of said modulated radio frequency carrier signals wherein none of the signals of the first group having the same carrier frequency as any other;   means for selecting a second group of modulated radio frequency carrier signals wherein none of the signals o the second group have the same carrier frequency as any other;   means for modulating one of said optical signals with the modulated radio frequency carrier signals of said first group; and   means for modulating another of said optical signals with the modulating radio frequency carrier signals of said second group.   
     
     
       10. A method for transmitting a plurality of radio frequency channels covering more than one octave of bandwidth from a first location to a second location, said method comprising the steps of: selecting two or more groups of contiguous radio frequency channels, each of said groups covering a bandwidth of less than one octave;   generating a plurality of optical signals of different wavelengths at said first location wherein each of said optical signals corresponds to at least one group of radio frequency channels;   modulating the intensity of each optical signal with the radio frequency channels of its respective group;   transmitting said resulting modulated optical signals to the second location via a signal optical link; and   demodulating each transmitted optical signal at the second location into its respective group of radio frequency channels.   
     
     
       11. A method of transmitting a plurality of channels of information from a first location to a second location said method comprising the steps of: defining two or more groups of channels wherein each channel is assigned to at least one of said groups;   modulating a radio frequency carrier signal with each channel in each group wherein each radio frequency carrier signal uniquely identifies one channel in a group;   generating a plurality of optical signals of different wavelengths, each corresponding to one of said groups of channels;   amplitude modulating each of said optical signals with the modulated radio frequency carriers corresponding to its respective group of channels;   transmitting each of said optical signals to the second location via a signal optical link;   demodulating each of said optical signals at the second location into its respective modulated radio frequency carrier signals;   converting at least one of said modulated radio frequency carrier signals to a different frequency band of carrier signals which does not overlap with any other transmitted radio frequency carrier signals; and   combining the resulting modulated radio frequency carrier signals in a single signal.